Several qualitative and quantitative diagnostic tests have developed in the clinical field utilizing a reflectometer for measuring optical radiation reflected from a test element. Reflectometers have been constructed featuring optical arrangements of lenses, filters, aperatures, a radiation source, and detector. Examples are described in U.S. Pat. Nos. 4,219,529, 4,224,032 and 3,536,927. In such arrangements, the separate components of the reflectometer must be accurately positioned and mounted to insure proper light path alignment and focusing. Often, problems arise with initially positioning and subsequently maintaining the proper mounting as the reflectometer is transported and operated. Furthermore, no provision is made to exclude the detection of specular reflectance which represents a significant noise factor when highly accurate and precise measurements of a selected analyte in a sample is needed.
One reflectometer devised to avoid these problems is disclosed in U.S. Pat. No. 4,518,259 to Ward. A one-piece molded housing contains a radiation guide and a source means and detector means to detect reflectance from a test element which is removably positioned on the outside of the housing. The measured reflectance is substantially free of specular component. However, the optical arrangement requires that the detector be positioned directly opposite the supported test element.
Recent emphasis has been placed upon diagnostic devices which are portable for use in clinical environment or directly by the patient. Portability requires more than being just lightweight or small, the bulk and shape should be convenient to carry and use. A reflectometer for such a device must be sufficiently compact. One example is the reflectometer disclosed in U.S. Pat. No. 4,552,458 to Lowne which supports and positions a test element in a predetermined, generally horizontal plane to avoid run off of the sample into the reflectometer. Light is reflected from a source to the test sample along a first path. From the test sample, the diffusely reflecting light is directed to a detector along a second path. The first and second paths must not lie in a common plane.
In addition to the space restriction, a single-use diagnostic device needs a reflectometer which is also inexpensive to manufacture since the device is disposable. The reflectometer may also be needed to perform a simultaneous analysis on more than one diagnostic assay or more than one test area or both. Even a reusable reflectometer may be needed to perform analysis on more than one test or sampling area using the same components. These needs have not been filled by the prior art.
Thus, a need exists in the field of diagnostics for a method and device for measurement of optical radiation which is sufficiently inexpensive, timely, efficient, durable, and reliable for use in a diagnostic device which permits point-of-care use by untrained individuals in locations such as the home, sites of medical emergencies, or locations other than a clinic. Whether the device is disposable or reusable, there is also a need to operate one or more channels simultaneously and reuse the same components for multiple test or sampling areas.